Human milk, and human milk-based products, are the preferred food for premature infants. Since the immune system of premature infants is relatively undeveloped, it is important that human milk-based products do not contain significant levels of bacteria, including Bacillus cereus. At the same time, it is important to minimize any alteration of the content of fat and protein in human milk, since these constituents are critical for the health and development of the premature infant.
The well known process of pasteurization has been used for many decades to kill bacteria in human milk. Bacillus cereus is an endospore forming bacteria and is often the predominant bacteria found in pasteurized human milk because it can survive the typical pasteurization process. Typical pasteurization processes (e.g., low or moderate temperatures for about 30 minutes) generally do not inactivate spore forming bacteria, such as Bacillus cereus. Unfortunately, the ultra-high temperatures and pressures needed in the pasteurization process to inactivate spore forming bacteria, such as Bacillus cereus, adversely affect the composition particularly the structure of fat and protein in human milk.
Various methods for producing non-human milk with a lowered bacterial count through the use of filtration are known in the art, however, none have found wide acceptance. The prior art methods generally suffer from either poor flow rates, rendering the method uneconomical on a large scale, or adversely affect the quality of the non-human milk, making the product unacceptable to the consumers.
Swedish patent publication No. 380,422 discloses a method in which non-human whole milk is divided into filtrate and concentrate fractions by microfiltration. The filtrate that passes through the pores of the filter (the size of the pores may range broadly from 0.1 micron-10 micron) consists of non-human milk with substantially reduced fat content and the concentrate, which is the fraction retained by the surface of the filter, consists of cream. Not only bacteria but also fat globules are substantially retained by the filter.
U.S. Pat. No. 5,064,674 relates to a method for making hypoallergenic non-human milk by ultrafiltration methods employing membranes that will allow molecules having a molecular weight of less than or equal to about 5 kDa to pass through. The excluded components that are trapped by the membrane include milk proteins, viable or non-viable bacteria, bacterial protein antigen, and milk fat. The filtrate collected from the ultrafiltration process therefore is free not only of bacteria and bacterial protein antigen, but also fat and milk protein, making the product unsuitable for use as non-human milk, per se.
Thus, the pores of filters used in the art to filter bacteria from milk compositions, while effective in sterilizing milk, will also remove fat and at least some of the proteins. Such a filter quickly becomes clogged by the trapped material; hence, the flow rate through the filter rapidly declines and the cost of such an inefficient process is generally prohibitive. Furthermore, because the filter retains fat and protein, the quality of the milk, is also adversely affected.
Thus, there is a need for an improved milk filtration processing method that can provide a sterile or more nearly sterile product while maintaining the nutritional content for human milk and human milk based products.